Drilling and producing offshore oil and gas wells includes the use of offshore facilities for the exploitation of undersea petroleum and natural gas deposits. A typical subsea system for drilling and producing offshore oil and gas can include the installation of a cap that commences when an operation, such as drilling a subsea well, is suspended or terminated.
Normally, a well is drilled for exploration or development, but once the well has been drilled and the rig is ready to move off location or move to another well, the blow-out preventer (BOP) is disconnected from the wellhead. The seal pocket on the wellhead would now be exposed and vulnerable to falling foreign objects. Typically, a subsea well can cost several millions of dollars to drill. Thus, leaving the wellhead exposed to damage from falling objects or other intruders could result in a loss of severe financial damage, as well as the loss of seal integrity and thereby render the wellhead useless.
When a wellsite is abandoned or temporarily suspended, it is desirable to protect the wellhead. During the installation of a subsea flow line, the drilling of a subsea well, the drilling of a mudline suspension well or the installation of a subsea tree, it may be necessary to suspend the operation due to inclement weather or requirement of additional equipment. When the operations have been suspended or completed, the end or top of the pipe or equipment has a seal area or a profile that needs to be protected from foreign objects, damage and/or marine growth. These seals, surfaces and profiles have varied outer and inner diameters, shapes and lengths. They also may contain seal pockets or integral components that need to be protected from corrosion and/or marine growth.
Thus, because of the potential for enormous loss of time and money and the need for protection on multiple structure profiles, it is desirable to have a cap for a subsea structure. For example, a tree cap can serve as a secondary pressure barrier on a subsea tree. There are a number of issues that could arise if these structures are not protected.
Also, hydrates can form beneath the tree caps, and methanol injection is required to dissolve these hydrates. Where water is present in gas being produced from a subterranean formation, the problem of gas hydrate formation exists. Often gas produced from a subterranean formation is saturated with water, thus that formation of gas hydrates poses a very significant problem. Hydrates are a solid, complex compound of hydrocarbons and water. Once a hydrate blockage occurs, pressure builds behind the hydrate blockage, which causes additional hydrates to form as a result of the increased pressure. Methanol can be injected to help further dissolve and prevent hydrate formation. Other chemicals can be injected into the flow lines.
Additionally, one of the most prominent characteristics of currently available protective coverings for subsea structures is that the size and shape of the covering must be closely matched to the size and shape of the subsea structure to enable the covering to mate with and latch to the structure. This design constraint means that there must be different coverings for different applications and the mating/latching requirements mean that the covering is much more expensive to manufacture and maintain.
In general, the approach of the prior art has been to focus on a particular aspect of protection that is very structure-dependent, costly to manufacture, and complex to operate. It would, therefore, be a significant advancement in the art and it is an object of the present invention to provide an improved cap that is simple to manufacture, install and remove. In addition, as the offshore oil industry moves to deeper and deeper depths, the time it takes to lower or retrieve the tree cap with drill pipe will cost a well operator thousands of dollars in rig time alone. Thus, it is desirable to have a tree caps and debris caps with flexibility for installation, retrieval, and operation.